<template>
  <div class="pagination">
    <!-- 左边 -->
    <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo',1)" :class="{active:pageNo==1}">1</button>
    <button v-if="startNumAndEndNum.start > 2">···</button>
    <!-- 中间部分 -->
    <button v-for="(page,index) in startNumAndEndNum.end" :key="index" v-if="page >= startNumAndEndNum.start" @click="$emit('getPageNo',page)" :class="{active:pageNo==page}">{{page}}</button>
    <!-- 右边 -->
    <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
    <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo',totalPage)" :class="{active:pageNo==totalPage}">{{totalPage}}</button>
    <button :disabled="pageNo==totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>
    
    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    props:['pageNo','pageSize','total','continues'],
    computed:{
      // 总共多少页
      totalPage(){
        // 向上取整
        return Math.ceil(this.total/this.pageSize)
      },
      // 页码的起始数字和结束数字
      startNumAndEndNum(){
        const {continues,pageNo,totalPage} = this
        let start = 0 ,end = 0
        // 连续页码数大于总页数（不正常现象）
        if(continues > totalPage){
          start = 1
          end = totalPage
        }else{
          // 连续页码数小于总页数（正常现象）
          start = pageNo - parseInt(continues/2)
          end = pageNo + parseInt(continues/2)
          // 不正常现象
          if(start < 1){
            start = 1
            end = continues
          }
          if(end > totalPage){
            start = totalPage - continues + 1
            end = totalPage
          }
        }
        return {start,end}
      }
    }
  }
</script>

<style lang="less" scoped>
  .pagination {
      text-align: center;
    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }
  .active {
    background: skyblue;
  }
</style>